A new primate model for the study of intravenous thrombotic potential and its modification

In vivo fluorescence imaging of large-vessel thrombosis in mice

OBJECTIVE

Experimental studies of large-vessel thrombosis have been adapted for applications in mice, but they proffer limited quantifiable information in outcome measures. This study presents a novel approach for evaluating large-vessel thrombogenesis with temporally/spatially quantifiable measures and normalization methods for interanimal comparisons.

METHODS AND RESULTS

Shuttered, beam-expanded lasers provided uniform narrow-wavelength illumination of a ×100 microsurgical field with a large depth of focus. Thrombosis was generated in murine carotid arteries and femoral veins by brief vascular surface electrolytic injury. Thrombus-targeting fluorophores were injected systemically and subsequently localized at the site of thrombus induction. A low-light digital video camera with filter wheel provided target-specific image acquisition over a 60-minute interval. Platelets accumulated with a subsequent fibrin border emerging to stabilize the clot in both arteries and veins. Coagulation enzyme complexes colocalized with fibrin deposition. Large arteries underwent cyclic massive thromboembolization, whereas veins showed gradual shedding of microemboli and clot contraction. Systemic administration of fibrin- and platelet-inhibiting compounds reduced their respective targets but also often inhibited their clotting counterparts (platelets and fibrin, respectively) in both arteries and veins.

CONCLUSION

Intermediate-level magnified image capture represents a novel approach for analysis of fluorescence-based in vivo imaging, with quantitative application to the study of large-vessel thrombosis.

[Leiomyosarcoma of the inferior vena cava]

Leiomyosarcomas of the inferior vena cava are rare and the clinical symptoms unspecific. We report a case of leiomyosarcoma of the inferior vena cava in an 82-year-old woman presenting with weight loss and abdominal pain. Following elaborate preoperative examinations, surgical resection was performed and the inferior vena cava was reconstructed. Clinical signs, diagnosis, therapy, and prognosis are discussed.

Animal models for the study of lower extremity chronic venous disease: lessons learned and future needs

The purpose of this review is to define animal models of chronic venous disease and to demonstrate how animal studies can impact our understanding and treatment of this disorder. To this end an extensive literature search was conducted highlighting potential animal models of chronic lower extremity venous disease. Scientific investigations using animals to study particular aspects of this disease are also reviewed. This review was conducted by members of the Committee on Research of the American Venous Forum to help provide direction for future venous research endeavors. Useful models of chronic venous occlusive disease involve controlled ligation of a major lower limb vein and multiple tributaries. Such a model can provide sustained venous hypertension and studies using this model have confirmed that an isodiametric graft can provide early hemodynamic relief. Models of primary, postphlebitic, and isolated chronic deep venous insufficiency are available for study. Valve repair or transplantation can positively impact the insufficiency observed in these models. Investigations into valve substitutes have generally been disappointing or are undergoing early evaluation. In conclusion, animal models for the study of some aspects of chronic venous disease do exist and have already affected our clinical approach to patients. The scientific study of basic pathophysiology, diagnostics, end-organ response, and long-term surgical treatments of this disorder in well-controlled animal experiments have not been conducted.

Effects of heparin, desmopressin, and isovolemic hemodilution with dextran on thrombus formation in synthetic vessel grafts inserted into the vena cava of the rabbit

The objective of this study was to investigate the effects of isovolemic hemodilution with dextran-70 on thrombus formation and blood flow in synthetic venous vessel grafts. Polytetrafluoroethylene grafts (length, 11 mm; inner diameter, 3 mm) were inserted into the vena cava of rabbits. Six groups were studied: (1) the control group; (2) animals that underwent isovolemic hemodilution with dextran-70 to a hematocrit of about 30%; (3) animals that underwent isovolemic dextran hemodilution combined with a bolus injection of heparin; (4) animals that underwent heparin treatment only; (5) animals that underwent isovolemic dextran hemodilution combined with infusion of desmopressin; and (6) animals that underwent an identical treatment to group 3 but with a 2-week, instead of a 2-day, follow-up. Vena cava blood flow was measured before and after hemodilution and graft insertion and at the termination of the experiments at 2 days (groups 1 to 5) and 2 weeks (group 6) after surgery. Graft patency and thrombus mass weight were evaluated. In the control group, most of the vessels occluded within 2 days. Hemodilution with dextran improved blood flow and reduced thrombus mass weight significantly. Desmopressin, which increases factor VIII, did not influence the effects of hemodilution with dextran, which suggests that the effects of dextran are not mediated by a reduction in the level of this coagulation factor. A single bolus dose of heparin did not reduce thrombus formation in the grafts but did potentiate the effects of isovolemic hemodilution on thrombus mass and graft blood flow. We conclude that isovolemic dextran hemodilution combined with a single bolus of heparin had beneficial long-lasting effects. The grafts in groups 3 and 6 were all patent.

The reliability of thrombotic tendency measured by intravascular wires in the rat

The objective was to determine if the amount of thrombus on two adjacent wires in an artery or in a vein was similar, and whether an upstream wire affected thrombosis on the downstream wire. Two 2 cm platinum wires were placed at adjoining sites in the abdominal vena cava and a further 2 in the abdominal aorta in 26 male and 24 female rats. In the artery, mean thrombus weight on the aortic downstream wire, set where the vessel is narrow, was significantly (p < 0.001) less than on the upstream wire, but the two correlated fairly well correlation coefficient (r = 0.608). In the vein, mean thrombus weight deposited in 1 hour was comparable on the pairs of wires both in males (r = 0.819) and females (r = 0.805). The mean downstream thrombus was slightly (10%) heavier than the upstream one both in males and females, a possible effect of vessel diameter, or of an activation by the upstream wire of thrombosis on the downstream one. An experiment to clarify that issue showed mean downstream venous thrombus to be again heavier than mean up-stream in both sexes (22 males, 30 females), and heavier than in controls in which no upstream wire was inserted. The platinum wire venous model seems to measure individual thrombotic response in a reasonably reproducible way in the rat. Upstream venous wire appears to activate thrombosis downstream from it by some 10%.

The anticoagulant, antithrombotic and haemorrhagic effect of long-term warfarin on experimental venous and arterial thrombosis in the rat

The amount of thrombus formed in one hour, on standard platinum wire in aorta and vena cava of 48 control and 96 warfarin treated rats of both sexes, was measured. Warfarin was given in varying doses (0.1-0.18 mg/kg) for ten consecutive days before operation to enable the coagulation factors to stabilize. Factors II, VII and X levels as well as prothrombin time (PT) values were obtained for each animal. Factor levels and PT ratio were related to reduction in arterial and venous thrombus weight. The relation between reduction in thrombus weight and depletion in coagulation factor levels was best for factor II and fairly good for factor X at all levels of anticoagulation. All animals which were haemorrhagic had factor II levels of below 15%, with a mean of 8%. At low warfarin dosage a significant reduction of thrombus (> 30%) went undetected by any test, but was least frequently undetected by factor II and most frequently undetected by PT. All rats with diminished thrombus had at least one factor depleted. Haemorrhagic animals were found with any PT ratio in excess of unity. Factor II reflected antithrombotic and haemorrhagic effects of warfarin much better than factors X, VII, or PT.

Pharmacologic intervention to prevent graft failure

Lower extremity vascular grafts, either vein or synthetic, fail for diverse reasons. Technical defects or poor surgical judgment doom a graft beyond any benefit pharmacotherapy can offer. Graft failure due to spontaneous thrombosis particularly affects prosthetic conduits, and use of antiplatelet agents (dextran, ASA) or anticoagulants (heparin, warfarin) is probably useful in this setting. An effective way to inhibit vein graft or anastomotic intimal hyperplasia remains elusive. Perhaps the most permanent and longstanding influence on lower extremity graft survival can be made through risk factor intervention aimed at arresting the progression of atherosclerosis. Aggressive treatment of hyperlipidemia, hypertension, smoking, and other known risk factors should be routinely and aggressively pursued in patients with lower extremity grafts, either autogenous or prosthetic. Lower extremity graft patency is optimally ensured by technically adept insertion of a proper autologous conduit in a well-selected patient. Pharmacotherapy may have a significant adjunctive role in the maintenance of graft patency, especially in high-risk settings such as limb salvage with associated poor outflow, a marginal vein graft, or the obligatory use of prosthetic material.